Controllably tuning properties of a fluid using modified nanoparticles

ABSTRACT

Properties of a base fluid may be controllably tuned to a pre-determined range of measurements by adding modified nanoparticles to a base fluid. The property to be modified may be or include, but is not limited to, electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof. The modified nanoparticles may be or include modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof. The base fluid may be or include, but is not limited to a non-aqueous based fluid, an aqueous fluid, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Patent Application No. 61/694502 filed Aug. 29, 2012; and is a Continuation-in-Part of U.S. application Ser. No. 13/903,692, entitled FLUIDS FOR USE WITH HIGH-FREQUENCY DOWNHOLE TOOLS, filed May 28, 2013; which is a continuation-in-part of U.S. patent application Ser. No. 13/545,706, entitled ELECTRICALLY CONDUCTIVE OIL-BASE FLUIDS FOR OIL AND GAS APPLICATIONS, filed on Jul. 10, 2012; which is a Continuation-in-Part of U.S. patent application Ser. No. 13/424,549, entitled “GRAPHENE-CONTAINING FLUIDS FOR OIL AND GAS EXPLORATION AND PRODUCTION”, filed on Mar. 20, 2012; which is a Continuation-in-Part of U.S. application Ser. No. 13/166,448, entitled NANOFLUIDS AND METHODS OF USE FOR DRILLING AND COMPLETION FLUIDS, filed Jun. 22, 2011, which claims the benefit of U.S. Provisional Application Ser. No. 61/359,111 filed Jun. 28, 2010, all of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to modified nanoparticles that may be added to a base fluid for controllably tuning at least one property of the base fluid where the property may be electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof.

BACKGROUND

Fluids used in the drilling, completion, production, and remediation of subterranean oil and gas wells are known. It will be appreciated that within the context herein, the term “fluid” also encompasses “drilling fluids”, “completion fluids”, “workover fluids”, “servicing fluids”, “production fluids”, and “remediation fluids”.

Drilling fluids are typically classified according to their base fluid. In water-based fluids, solid particles are suspended in a continuous phase consisting of water or brine. Oil can be emulsified in the water which is the continuous phase. “Water-based fluid” is used herein to include fluids having an aqueous continuous phase where the aqueous continuous phase can be all water or brine, an oil-in-water emulsion, or an oil-in-brine emulsion. Brine-based fluids, of course are water-based fluids, in which the aqueous component is brine.

Oil-based fluids are the opposite or inverse of water-based fluids. “Oil-based fluid” is used herein to include fluids having a non-aqueous continuous phase where the non-aqueous continuous phase is all oil, a non-aqueous fluid, a water-in-oil emulsion, a water-in-non-aqueous emulsion, a brine-in-oil emulsion, or a brine-in-non-aqueous emulsion. In oil-based fluids, solid particles are suspended in a continuous phase consisting of oil or another non-aqueous fluid. Water or brine can be emulsified in the oil; therefore, the oil is the continuous phase. In oil-based fluids, the oil may consist of any oil or water-immiscible fluid that may include, but is not limited to, diesel, mineral oil, esters, refinery cuts and blends, or alpha-olefins. Oil-based fluid as defined herein may also include synthetic-based fluids or muds (SBMs), which are synthetically produced rather than refined from naturally-occurring materials. Synthetic-based fluids often include, but are not necessarily limited to, olefin oligomers of ethylene, esters made from vegetable fatty acids and alcohols, ethers and polyethers made from alcohols and polyalcohols, paraffinic, or aromatic, hydrocarbons alkyl benzenes, terpenes and other natural products and mixtures of these types.

For some applications, in particular for the use of some wellbore imaging tools, it is important to reduce the electrical resistivity (which is equivalent to increase the electrical conductivity) of the oil-based fluid in a controllable manner. It would be desirable if fluid compositions and methods could be devised to controllably modify or tune the electrical conductivity, dielectric strength, and/or the thermal conductivity of the oil-based or non-aqueous liquid-based drilling, completion, production, and remediation fluids and thereby allow for better utilization of resistivity logging tools.

There are a variety of functions and characteristics that are expected of completion fluids. The completion fluid may be placed in a well to facilitate final operations prior to initiation of production. Completion fluids are typically brines, such as chlorides, bromides, formates, but may be any non-damaging fluid having proper density and flow characteristics. Suitable salts for forming the brines include, but are not necessarily limited to, sodium chloride, calcium chloride, zinc chloride, potassium chloride, potassium bromide, sodium bromide, calcium bromide, zinc bromide, sodium formate, potassium formate, ammonium formate, cesium formate, and mixtures thereof.

Chemical compatibility of the completion fluid with the reservoir formation and fluids is key. Chemical additives, such as polymers and surfactants are known in the art for being introduced to the brines used in well servicing fluids for various reasons that include, but are not limited to, increasing viscosity, and increasing the density of the brine. Water-thickening polymers serve to increase the viscosity of the brines and thus retard the migration of the brines into the formation and lift drilled solids from the wellbore. A regular drilling fluid is usually not compatible for completion operations because of its solid content, pH, and ionic composition.

Completion fluids also help place certain completion-related equipment, such as gravel packs, without damaging the producing subterranean formation zones. Conventional drilling fluids are rarely suitable for completion operations due to their solids content, pH, and ionic composition. The completion fluid should be chemically compatible with the subterranean reservoir formation and its fluids. Controllably modifying at least one property, such as but not limited to electrical conductivity, dielectric strength, and/or thermal conductivity of completion fluids may allow the use of resistivity logging tools for facilitating final operations.

Servicing fluids, such as remediation fluids, workover fluids, and the like, have several functions and characteristics necessary for repairing a damaged well. Such fluids may be used for breaking emulsions already formed and for removing formation damage that may have occurred during the drilling, completion and/or production operations. The terms “remedial operations” and “remediate” are defined herein to include a lowering of the viscosity of gel damage and/or the partial or complete removal of damage of any type from a subterranean formation. Similarly, the term “remediation fluid” is defined herein to include any fluid that may be useful in remedial operations.

A stimulation fluid may be a treatment fluid prepared to stimulate, restore, or enhance the productivity of a well, such as fracturing fluids and/or matrix stimulation fluids in one non-limiting example.

Before performing remedial operations, the production of the well must be stopped, as well as the pressure of the reservoir contained. To do this, any tubing-casing packers may be unseated, and then servicing fluids are run down the tubing-casing annulus and up the tubing string. These servicing fluids aid in balancing the pressure of the reservoir and prevent the influx of any reservoir fluids. The tubing may be removed from the well once the well pressure is under control. Tools typically used for remedial operations include wireline tools, packers, perforating guns, flow-rate sensors, electric logging sondes, etc.

Despite the ability to measure deeper into the formation, the resolution of these tools is still strongly affected by the properties of the fluid within which the imaging tool is used. In order to meet the challenges encountered in the imaging of drilled formations, advanced electrical imaging tools have been developed that operate within a fluid having modified electrical conductivity and modified dielectric constant to obtain a signal at a desired frequency. Different tools require different fluid properties for maximizing the performance of the tools. For instance, tools that operate at low-frequencies (e.g. 10 kHz or lower) require fluids having a low-resistivity; whereas, tools that operate at high-frequency (e.g. 100 kHz or higher) require fluids having a high resistivity and a high dielectric constant.

It would be desirable if the fluid compositions and methods for using such fluids could be controllably tuned or tailored to improve the electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof to enhance the performance of resistivity logging tools in one non-limiting example.

SUMMARY

There is provided, in one form, a method for controllably tuning at least one property of a base fluid, such as but not limited to electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof. Modified nanoparticles may be added to the base fluid. The modified nanoparticles may be or include, but are not limited to, modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof. The modified nanoparticles may be modified by a method, such as but not limited to chemical modification, covalent modification, functionalization, ionic associations and combinations thereof. The base fluid may be or include, but is not limited to a non-aqueous base fluid, an aqueous base fluid, and combinations thereof.

There is further provided in another non-limiting embodiment where a tuned fluid may be circulated in a subterranean reservoir wellbore, and the fluid may improve performance of a downhole tool as compared to an otherwise identical fluid absent the modified nanoparticles. The tuned fluid may have or include a base fluid and an effective amount of modified nanoparticles to improve at least one property of the fluid. The modified nanoparticles may be or include modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof. The modified nanoparticles may be modified by a method, such as chemical modification, covalent modification, functionalization, ionic associations, and combinations thereof. The base fluid may include a non-aqueous based fluid, an aqueous based fluid, and combinations thereof.

In another form, there is provided a fluid composition that may include a base fluid and modified nanoparticles. The base fluid may be or include, but is not limited to a non-aqueous base fluid, an aqueous base fluid, and combinations thereof. The modified nanoparticles may be or include, but are not limited to, modified graphene nanoparticles, modified nanotubes, modified graphene platelets, single-walled carbon nanotubes, multiwalled carbon nanotubes, double-walled carbon nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof. The modified nanoparticles may be modified by a method, such as but not limited to chemical modification, covalent modification, functionalization, ionic associations, and combinations thereof. The fluid composition may have a resistivity ranging from about 0.02 ohm-m to about 1,000,000 ohm-m, a thermal conductivity ranging from about 0.1 W/m-K to about 1.2 W/m-K, a dielectric strength ranging from about 6 MV/m to about 100 MV/m, and combinations thereof.

The modified nanoparticles appear to alter the electrical properties of the base fluid for better use of electrical logging while drilling and wireline tools.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating two reactions where each reaction causes a weight loss of the graphitic nanoparticles as measured by thermogravimetric analysis (TGA); and

FIG. 2 is a graph illustrating the average thermal conductivity of graphitic nanoparticles having increased amounts of oxidant.

DETAILED DESCRIPTION

It has been discovered that a base fluid may be controllably tuned by adding modified nanoparticles to the base fluid such that the use of a downhole tool may be permitted or improved in non-aqueous fluids, e.g. a resistivity logging tool. These tools are typically only used in aqueous fluids, such as water-based fluids in a non-limiting example, because resistivity logging tools require the fluid in the wellbore to be electrically conductive. The dispersion of modified nano-materials, into at least one phase of the non-aqueous fluid, such as the continuous phase of the non-aqueous fluid in a non-limiting embodiment, may controllably tune at least one property of the non-aqueous base fluid. Properties of the base fluid that may be altered include, but are not limited to, electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof.

This is important because many downhole tools, such as imaging tools in a non-limiting example, utilize an alternating current (a.c.) with a high frequency, so the fluids used in conjunction with these tools need to have a particular electrical conductivity and have a particular dielectric constant for the tool to function and to achieve maximum resolution. The properties of the fluid may be modified by adding electrically conductive nanoparticles and/or non-electrically conductive nanoparticles to the base fluid, such that the use of a downhole tool, such as a measuring while drilling tool, in a non-limiting example, in non-aqueous fluids may be permitted or perform better. The type of nanoparticles depends on the desired properties of the fluid.

The electrical conductivity and/or dielectric constant of the fluid are important in relation to the high frequency downhole tools because these tools are designed to operate with fluids having properties within a certain range of values. If the actual value of dielectric constant or electrical conductivity (the inverse of resistivity) is outside a particular range, real changes in resistivity of formation are not detected either because of a very low signal to noise ratio, or because preferential paths for current transmission may develop. In both cases, the capability of discrimination between zones with different resistivity becomes compromised, and resolution deteriorates; eventually, the high frequency downhole tool does not properly function in this type of environment.

In one non-limiting example, the resolution from a high frequency downhole tool, such as a measuring-while-drilling tool, increases when altering the resistivity and/or the dielectric strength according to the formula [resistivity×(dielectric strength)²]. In other words, the resolution of the tools may be improved by altering the electrical conductivity (the inverse of resistivity) or the dielectric constant of the fluid by adding the nanoparticles to the base fluid. For example, a fluid for use with a high frequency downhole tool may have at least one property, such as but not limited to, a relative dielectric constant ranging from about 5 to about 10,000, an electrical conductivity ranging from about 1×10⁻⁶ S/m to about 1 S/m, and combinations thereof.

The properties of the fluid composition, i.e. where the fluid composition includes at least the base fluid and the modified nanoparticles, may be determined by the content and the inherent properties of the dispersed phase content, which may be tailored to achieve the desired values of electrical conductivity, dielectric strength, and/or thermal conductivity.

The modified nanoparticles to be added to the base fluid may be modified graphene nanoparticles, modified graphene platelets, modified graphene oxide, modified nanotubes, modified nanorods, modified nanoplatelets, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof. The modified nanotubes, modified nanorods, and/or the modified nanoplatelets may be metallic and/or ceramic in an alternative embodiment. In one non-limiting embodiment, the modified nanotubes are modified carbon nanotubes. “Modified nanoparticles” is defined herein to mean that the nanoparticles are altered or engineered to cause the base fluid to acquire a pre-designated range with respect to electrical conductivity, dielectric strength, and/or thermal conductivity.

The base fluid may be a non-aqueous fluid, an aqueous fluid, and combinations thereof. The non-aqueous fluid may be an all oil fluid, brine-in-oil emulsion, or a water-in-oil emulsion, and combinations thereof. In a non-limiting example, the base fluid may be selected from the group consisting of a completion fluid, a production fluid, a servicing fluid, a stimulation fluid, and combinations thereof.

The amount of modified nanoparticles added to the base fluid may range from about 0.0001 wt % to about 15 wt % of the total fluid. In a non-limiting embodiment, the modified nanoparticles may be added in an amount ranging from about 0.001 wt % independently to about 5 wt %, alternatively from about 0.01 wt % independently to about 1 wt %. “Independently” as used herein means that any lower threshold may be combined with any upper threshold to define an acceptable alternative range.

The modified properties of the fluid may enable better use of the downhole tools as compared to usage of the tools without modification of these properties by the addition of the modified nanoparticles. Moreover, the modified properties of the fluid may improve the performance of the downhole tools by improving the resolution of these tools as compared to an otherwise identical fluid absent the nanoparticles. “Independently” as used herein means that any lower threshold may be combined with any upper threshold to define an acceptable alternative range.

The modified nanoparticles may be dispersed in the base fluid so that the base fluid may acquire an electrical resistivity range of from about 0.02 ohm-m independently to about 1,000,000 ohm-m in one non-limiting embodiment. In an alternative embodiment, the electrical resistivity range may be from about 0.2 ohm-m independently to about 10,000 ohm-m, or from about 2 ohm-m independently to about 1,000 ohm-m. Controllably tuning the electrical resistivity of the base fluid may improve the performance of a downhole tool as compared to an otherwise identical fluid absent the nanoparticles.

The nanoparticles may be modified and dispersed in the base fluid so that the base fluid may acquire a thermal conductivity ranging from about 0.1 W/m-K to about 1.2 W/m-K in one non-limiting embodiment. In an alternative embodiment, the thermal conductivity may range from about 0.15 W/m-K independently to about 1.1 W/m-K, or from about 0.2 W/m-K independently to about 1 W/m-K in another non-limiting embodiment.

The nanoparticles may be modified and dispersed in the base fluid so that the base fluid may acquire a dielectric strength ranging from about 6 MV/m to about 100 MV/m, alternatively greater than about 12 MV/m, greater than about 65 MV/m, or greater than about 90 MV/m in another non-limiting embodiment.

The nanoparticles may be modified and dispersed in the base fluid so that the base fluid may acquire a breakdown potential ranging from about 12 kV independently to about 50 kV, alternatively from about 16 kV independently to about 40 kV, or from about 20 kV independently to about 35 kV in another non-limiting embodiment,

Oil-based fluids typically have minimal conductivity, if any conductivity at all. The modified nanoparticles allow for controllably tuning the thermal conductivity, the dielectric strength, and/or the breakdown potential of the fluid, which may allow for better usage of resistivity logging tools, and wire-line tools within oil-based fluids, and for better dispersion of heat around these wire-line tools because the fluid may act as a conduit, and the fluid does not heat up as quickly. Alternatively, the nanoparticle fluid may temporarily dissipate heat within the reservoir.

In addition to the modified nanoparticles to controllably tune at least one property of a base fluid, the modification and/or functionalization of the nanoparticles may improve the dispersibility of the nanoparticles in a non-aqueous fluid by stabilizing the modified nanoparticles in suspension, which avoids undesirable flocculation as compared with otherwise identical nanoparticles that have not been modified or functionalized. In one non-limiting embodiment, it is desirable that the properties of the fluid be approximately uniform, which requires the distribution of the nanoparticles to be approximately uniform. If the nanoparticles flocculate, drop out, or precipitate, the modified or improved properties of the fluid may change.

Graphene is an allotrope of carbon, whose structure is a hexagonal shape and forms a planar sheet of sp²-bonded carbon atoms that are densely packed in a 2-dimensional honeycomb crystal lattice. The 2-D morphology of the graphene nanoparticles is of utmost importance when carrying out the useful applications relevant to the graphene nanoparticles. The applications of graphite, the 3-D version of graphene, are not equivalent to the 2-D applications of graphene. The graphene may have at least one graphene sheet, and each graphene platelet may have a thickness no greater than about 100 nm. The term “graphene” is used herein to include particles that may contain more than one atomic plane, but still with a layered morphology, i.e. one in which one of the dimensions is significantly smaller than the other two, and also may include any graphene that has been chemically modified, physically modified, covalently modified, functionally modified, and combinations thereof. Although there is no exact maximum number of layers in graphene, the number of layers may range from about 2 layers independently to about 100 layers, alternatively from about 4 layers independently to about 75 layers, or from about 6 layers independently to about 20 layers in another non-limiting embodiment.

Graphene may be in the form of one-atomic layer thick or multi-atomic layer thick platelets. Graphene platelets may have in-plane dimensions ranging from sub-micrometer to about 100 s micrometers. These types of graphene platelets share many of the same characteristics as carbon nanotubes. The graphene platelet chemical structure makes it easier to functionalize or modify the graphene platelet for enhanced dispersion in polymers. Graphene platelets provide electrical conductivity that is similar to copper, but the density of the graphene platelets is about four times less than that of copper, which allows for lighter materials. The graphene platelets are stronger than steel and have a surface area larger than that of carbon nanotubes.

The properties of graphene have been measured and compare well with those of carbon nanotubes. The 2-D morphology, however, provides significant benefits when dispersed in complex fluids, such as multi-phasic fluids or emulsions. The graphene may be engineered and/or modified and then dispersed within the non-conducting phase of the base fluid, to achieve the desired properties.

Carbon nanotubes are defined herein as allotropes of carbon consisting of one or several single-atomic layers of graphene rolled into a cylindrical nanostructure. Nanotubes may be single-walled, double-walled or multi-walled.

Nanodiamonds have a rounded shape with an active surface and a diamond-like hardness. Nanodiamonds may have wear resistance, may be resistant to steel corrosion, and/or may have angstrom finishes of polished surfaces, yet have the physical characteristics similar to rubber. Nanodiamonds may be created by detonating trinitrotoluene (TNT) and 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) and then gathering the remaining soot. The soot left over may contain tiny diamonds. The size of these nanodiamonds may range in size from about 1 nm independently to about 20 nm, or from about 4 nm independently to about 10 nm.

In the present context, the modified nanoparticles may have at least one dimension less than about 50 nm, although other dimensions may be larger than this. In a non-limiting embodiment, the modified nanoparticles may have one dimension less than about 30 nm, or alternatively less than about 10 nm. In one non-limiting instance, the smallest dimension of the modified nanoparticles may be less than about 5 nm, but another dimension of the same modified nanoparticle may be much longer than about 100 nm, for instance about 25,000 nm or more. Such modified nanoparticles would be within the scope of the fluids herein.

Nanoparticles typically have at least one dimension less than about 100 nm (one hundred nanometers). While materials on a micron scale have properties similar to the larger materials from which they are derived, assuming homogeneous composition, the same is not true of nanoparticles. An immediate example is the very large interfacial or surface area per volume for nanoparticles. The consequence of this phenomenon is a very large potential for interaction with other matter, as a function of volume. For nanoparticles, the surface area may be up to 1800 m²/g. Additionally, because of the very large surface area to volume present with graphene, it is expected that in most, if not all cases, much less proportion of the modified graphene nanoparticles need be employed relative to micron-sized additives conventionally used to achieve or accomplish a similar effect.

Nevertheless, it should be understood that surface-modified nanoparticles may find utility in the compositions and methods herein. “Surface-modification” is defined here as the process of altering or modifying the surface properties of a nanoparticle by any means, including but not limited to physical, chemical, and electrochemical means, and with the intent to provide a unique desirable property or combination of properties to the surface of the nanoparticle, which differs from the properties of the surface of the unprocessed nanoparticle.

The modified nanoparticles may be, but not limited to, chemically-modified nanoparticles, covalently-modified nanoparticles, physically modified nanoparticles, functionalized nanoparticles, and combinations thereof. The nanoparticles may be functionally modified to introduce chemical functional groups thereon, for instance by reacting graphene nanoparticles with a peroxide such as diacyl peroxide to add acyl groups that are in turn reacted with diamines to give amine functionality, which may be further reacted. “Functionalized nanoparticles” are defined herein as those which have had their edges, ends or surfaces modified to contain at least one functional group including, but not necessarily limited to, sulfonate, sulfate, sulfosuccinate, thiosulfate, succinate, carboxylate, hydroxyl, glucoside, ethoxylate, propoxylate, phosphate, ether, amines, amides, ethoxylate-propoxylate, an alkyl, an alkenyl, a phenyl, a benzyl, a perfluoro, thiol, an ester, an epoxy, a keto, a lactone, a metal, an organo-metallic group, an oligomer, a polymer, or combinations thereof.

Introduction of functional groups by derivatizing the olefinic functionality associated with the nanoparticles may be affected by any of numerous known methods for direct carbon-carbon bond formation to an olefinic bond, or by linking to a functional group derived from an olefin. Exemplary methods of functionalizing may include, but are not limited to, reactions such as oxidation or oxidative cleavage of olefins to form alcohols, diols, or carbonyl groups including aldehydes, ketones, or carboxylic acids; diazotization of olefins proceeding by the Sandmeyer reaction; molecules having benzylic functional groups; use of transmetalated species with boron, zinc, or tin groups that react with e.g., aromatic halides in the presence of catalysts such as palladium, copper, or nickel, which proceed via mechanisms such as that of a Suzuki coupling reaction or the Stille reaction; pericyclic reactions (e.g., 3 or 4+2) or thermocyclic (2+2) cycloadditions of other olefins, dienes, heteroatom substituted olefins, and combinations thereof.

In one non-limiting embodiment, a nanodiamond may be functionalized by intercalation/metallization of the nanodiamond by treatment with a reactive metal, such as an alkali metal including lithium, sodium, potassium, and the like, to form an anionic intermediate. The anionic intermediate may be treated with a molecule capable of reacting with the metalized nanodiamond, such as a carbonyl-containing species (carbon dioxide, carboxylic acids, anhydrides, esters, amides, imides, etc.), an alkyl species having a leaving group such as a halide (Cl, Br, I), a tosylate, a mesylate, or other reactive esters such as alkyl halides, alkyl tosylates, etc, and combinations thereof.

It will be appreciated that the above methods are intended to illustrate the concept of introducing functional groups to a nanoparticle for purposes of forming modified nanoparticles, and should not be considered as limiting to such methods.

Prior to functionalization, the nanoparticle may be exfoliated. Exemplary exfoliation methods include, but are not necessarily limited to, those practiced in the art such as fluorination, acid intercalation, acid intercalation followed by thermal shock treatment, and the like. Exfoliation of the nanographene provides a nanographene having fewer layers than non-exfoliated nanographene.

The effective medium theory states that properties of materials or fluids comprising different phases can be estimated from the knowledge of the properties of the individual phases and their volumetric fraction in the mixture. In particular, if a conducting modified nanoparticle is dispersed in a dielectric fluid, the electrical conductivity of the dispersion will slowly increase for small additions of modified nanoparticles. As modified nanomaterials are continually added to the dispersion, the desired properties of the fluid composition changes, i.e. the base fluid may be controllably tuned with respect to the modification of the nanoparticles as well as the amount of modified nanoparticles added to the base fluid. For example, there is a strong correlation between increased conductivity and increased concentration of modified nanoparticles. This concentration is often referred to as the percolation limit. In another non-limiting example, there is a strong correlation between increased oxidant when modifying the nanoparticles and decreased thermal conductivity of the base fluid upon addition of the modified nanoparticles to the base fluid.

In the case of thermal conductivity of modified nanoparticles to the base fluid, or nanofluids, the percolation limit decreases with decreasing the size of the nanomaterials. This dependence of the percolation limit on the concentration of the modified nanoparticles holds for other fluid properties that depend on inter-particle average distance.

There is also a strong dependence on the shape of the modified nanoparticles dispersed within the phases for the percolation limit of modified nano-dispersions. The percolation limit shifts further towards lower concentrations of the dispersed phase if the nanoparticles have characteristic 2-D (platelets) or 1-D (nanotubes or nanorods) morphology. Thus, the amount of 2-D or 1-D nanomaterials necessary to achieve a certain change in property is significantly smaller than the amount of 3-D nanomaterials that would be required to accomplish a similar effect.

In one sense, such fluids have made use of nanoparticles for many years, since the clays commonly used in drilling fluids are naturally-occurring, 1 nm thick discs of aluminosilicates. Such modified nanoparticles exhibit extraordinary rheological properties in water and oil. However, in contrast, the modified nanoparticles that are the main topic herein are synthetically modified or engineered nanoparticles where size, shape and chemical composition are carefully controlled. The modified nanoparticles may then be added into a base fluid for controllably tuning a base fluid to achieve a pre-specified range for electrical conductivity, dielectric strength, and/or thermal conductivity.

In some cases, the modified nanoparticles may change the properties of the base fluids in which they reside, based on various stimuli including, but not necessarily limited to, temperature, pressure, rheology, pH, chemical composition, salinity, and the like. This is due to the fact that the modified nanoparticles can be custom designed on an atomic level to have very specific functional groups, and thus the modified nanoparticles react to a change in surroundings or conditions in a way that is beneficial. It should be understood that it is expected that modified nanoparticles may have more than one type of functional group, making them multifunctional. Multifunctional nanoparticles may be useful for simultaneous applications, in a non-limiting example of a fluid, lubricating the bit, increasing the temperature stability of the fluid, stabilizing the shale while drilling and provide low shear rate viscosity, while still obtaining or achieving a pre-specified range for electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof. In another non-restrictive embodiment, modified nanoparticles suitable for stabilizing shale include those having an electric charge that permits them to associate with the shale.

The nanoparticles may be used in conventional operations and challenging operations that require stable fluids for high temperature and pressure conditions (HTHP). Such fluids are expected to find uses in, but are not limited to reservoir operations including reservoir imaging, resistivity logging, drilling fluids, completion fluids, remediation fluids, reservoir stimulation fluids, cementing fractioning fluids, production fluids, and combinations thereof.

The use of surfactants together with the nanoparticles may form self-assembly structures that may enhance the thermodynamic, physical, and rheological properties of these types of fluids. It may be helpful in designing new fluids containing modified nanoparticles to match the amount of the modified nanoparticles with the proper surfactant/base fluid ratio to achieve the desired dispersion for a particular base fluid. Surfactants are generally considered optional, but may be used to improve the quality of the dispersion of the modified nanoparticles within the fluid. Such surfactants may be present in the base fluids in an amount ranging from about 0.01 wt % independently to about 15 wt %, alternatively from about 0.01 wt % independently to about 5 wt %.

Expected suitable surfactants may include, but are not necessarily limited to non-ionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants and zwitterionic surfactants, janus surfactants, and blends thereof. Suitable nonionic surfactants may include, but are not necessarily limited to, alkyl polyglycosides, sorbitan esters, methyl glucoside esters, amine ethoxylates, diamine ethoxylates, polyglycerol esters, alkyl ethoxylates, alcohols that have been polypropoxylated and/or polyethoxylated or both. Suitable anionic surfactants may include alkali metal alkyl sulfates, alkyl ether sulfonates, alkyl sulfonates, alkyl aryl sulfonates, linear and branched alkyl ether sulfates and sulfonates, alcohol polypropoxylated sulfates, alcohol polyethoxylated sulfates, alcohol polypropoxylated polyethoxylated sulfates, alkyl disulfonates, alkylaryl disulfonates, alkyl disulfates, alkyl sulfosuccinates, alkyl ether sulfates, linear and branched ether sulfates, alkali metal carboxylates, fatty acid carboxylates, and phosphate esters. Suitable cationic surfactants may include, but are not necessarily limited to, arginine methyl esters, alkanolamines and alkylenediamides. Suitable surfactants may also include surfactants containing a non-ionic spacer-arm central extension and an ionic or nonionic polar group. Other suitable surfactants may be dimeric or gemini surfactants, cleavable surfactants, janus surfactants, and extended surfactants (also called extended chain surfactants).

It is also anticipated that combinations of certain surfactants and modified nanoparticles will “self-assemble” into useful structures, similar to the way certain compositions containing surfactants self-assemble into liquid crystals of various different structures and orientations.

Covalent functionalization may include, but is not necessarily limited to, oxidation and subsequent chemical modification of oxidized nanoparticles, fluorination, free radical additions, addition of carbenes, nitrenes and other radicals, arylamine attachment via diazonium chemistry, and the like. Besides covalent functionalization, chemical functionality may be introduced by noncovalent functionalization, electrostatic interactions, π-π interactions and polymer interactions, such as wrapping a nanoparticle with a polymer, direct attachment of reactants to nanoparticles by attacking the sp² bonds, direct attachment to ends of nanoparticles or to the edges of the nanoparticles, and the like.

Benefits that may arise from modifying the nanoparticles to controllably tune at least one property of the drilling or completion fluids may include enabling the implementation of measuring tools based on resistivity with superior image resolution, and therefore improving the ability of the driller to improve its efficiency. It may also be conceivable that an electric signal will be able to be carried through the drilling fluids across longer distances, such as across widely spaced electrodes in or around the bottom-hole assembly, or even from the bottom of the wellbore to intermediate stations or the surface of the well. In addition, enhanced conductivity of the base fluid may form a conductive filter cake that highly improves real time high resolution logging processes, as compared with an otherwise identical fluid absent the modified nanoparticles.

FIG. 1 is a graph that corresponds with TABLE 1 below. FIG. 1 illustrates the weight loss (noted as WL in TABLE 1) of the graphitic nanoparticles having increased amounts of oxidant as measured by thermogravimetric analysis (TGA). A weight loss measurement is taken by using the TGA before the functionalization to the graphitic nanoparticles occurs and after the functionalization occurs. An increase in the measurement after the function correlates to the amount of functionalization that occurred with the graphitic nanoparticles. As the nanoparticles are modified with increased amounts of oxidant, the weight loss also increases. Weight loss appears to be most apparent between 0.50 grams of oxidant and 0.67 grams of oxidant.

TABLE 1 Sample Amt of Rxn WL after Thermal ID Oxidant time WL Functionalization Conductivity 1 1 0.5 h  57.61% 65.57% 0.2176 W/m-K 2 1  1 h 59.01% 65.78% 0.2125 W/m-K 3 1  3 h 71.85% 71.64% 0.2178 W/m-K 4 1  6 h 57.92% 71.87%  0.216 W/m-K 5 1 16 h 65.31% 82.68% 0.2056 W/m-K 6 0.33 16 h 22.12% 44.33% 0.4109 W/m-K 7 0.5 16 h 59.65% 46.18% 0.3617 W/m-K 8 0.67 16 h 47.49% 71.45% 0.2816 W/m-K

FIG. 2 is a graph illustrating the average thermal conductivity of the graphitic nanoparticles having increased amounts of oxidant. Here, the average thermal conductivity appears to decrease as nanoparticles are modified with increased amounts of oxidant; i.e. an inverse relationship.

The invention will be further described with respect to the following Examples which are not meant to limit the invention, but rather to further illustrate the various embodiments.

TABLE 2 Sample ID Carbon Core Thermal Conductivity Dielectric Strength 1 5.0 wt % 0.2056 W/m-K too viscous 2 2.5 wt % 0.1954 W/m-K not enough sample 3 3.5 wt % 0.2018 W/m-K 11.8 kV 4 1.75 wt %  0.1936 W/m-K 16.7 kV 5 2.5 wt % 0.1939 W/m-K 15.8 kV 6 1.25 wt %  0.1937 W/m-K 22.5 kV 7 1.5 wt % 0.1941 W/m-K 25.1 kV 8 0.5 wt % 0.1931 W/m-K 26.4 kV

EXAMPLES 1-8 Correspond to Table 2 Above EXAMPLE 1

Sample 1 included nanoparticles having a graphitic structure with a carbon core of about 5.0 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.2056 W/m-K. The fluid was too viscous to measure the dielectric strength.

EXAMPLE 2

Sample 2 included nanoparticles having a graphitic structure with a carbon core of about 2.5 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1954 W/m-K, and there was not enough fluid sample remaining to measure the dielectric strength.

EXAMPLE 3

Sample 3 included nanoparticles having a graphitic structure with a carbon core of about 3.5 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.2018 W/m-K, and the dielectric strength was about 11.8 kV.

EXAMPLE 4

Sample 4 included nanoparticles having a graphitic structure with a carbon core of about 1.75 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1936 W/m-K, and the dielectric strength was about 16.7 kV.

EXAMPLE 5

Sample 5 included nanoparticles having a graphitic structure with a carbon core of about 2.5 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1939 W/m-K, and the dielectric strength was about 15.8 kV.

EXAMPLE 6

Sample 6 included nanoparticles having a graphitic structure with a carbon core of about 1.25 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1937 W/m-K, and the dielectric strength was about 22.5 kV.

EXAMPLE 7

Sample 7 included nanoparticles having a graphitic structure with a carbon core of about 1.5 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1941 W/m-K, and the dielectric strength was about 25.1 kV.

EXAMPLE 8

Sample 8 included nanoparticles having a graphitic structure with a carbon core of about 0.5 wt %. The thermal conductivity of the base fluid prior to adding the modified nanoparticles to the base fluid was about 0.185 W/m-K, and the dielectric strength was about 35.4 kV. The thermal conductivity of the base fluid after adding the modified nanoparticles was about 0.1931 W/m-K, and the dielectric strength was about 26.4 kV.

In the foregoing specification, the invention has been described with reference to specific embodiments thereof, and has been described as effective in providing methods and compositions for controllably tuning or altering at least one property of a base fluid, such as but not limited to the electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof of the fluid. However, it will be evident that various modifications and changes can be made thereto without departing from the broader spirit or scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, specific base fluids, modified nanoparticles, and modifications falling within the claimed parameters, but not specifically identified or tried in a particular composition or method, are expected to be within the scope of this invention.

The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For instance, the method may consist of or consist essentially of tuning at least one property of a fluid by adding modified nanoparticles to the base fluid where the modified nanoparticles may include, but are not limited to modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof; the base fluid may be a non-aqueous based fluid, an aqueous based fluid, and combinations thereof.

The fluid composition may consist of or consist essentially of a base fluid and modified nanoparticles where the base fluid may be a non-aqueous base fluid, an aqueous base fluid, and combinations thereof; and where the modified nanoparticles may be or include modified graphene nanoparticles, modified nanotubes, modified graphene platelets, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof; and the fluid composition may have a resistivity ranging from about 0.02 ohm-m to about 1,000,000 ohm-m, a thermal conductivity ranging from about from about 0.1 W/m-K to about 1.2 W/m-K, a dielectric strength ranging from about 6 MV/m to about 100 MV/m, and combinations thereof.

The words “comprising” and “comprises” as used throughout the claims, are to be interpreted to mean “including but not limited to” and “includes but not limited to”, respectively. 

What is claimed is:
 1. A method for controllably improving at least one property of a fluid comprising: adding modified nanoparticles to a base fluid, wherein the modified nanoparticles are selected from the group consisting of modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof; wherein the modified nanoparticles are nanoparticles that were modified by a method selected from the group consisting of chemical modification, covalent modification, functionalization, ionic associations, and combinations thereof; and wherein the base fluid comprises a non-aqueous based fluid, an aqueous based fluid, and combinations thereof; and improving the at least one property selected from the group consisting of electrical conductivity, dielectric strength, thermal conductivity, and combinations thereof.
 2. The method of claim 1, wherein the fluid has a thermal conductivity ranging from about 0.1 W/m-K to about 1.2 W/m-K after adding the modified nanoparticles.
 3. The method of claim 1, wherein the fluid has a dielectric strength ranging from about 6 MV/m to about 100 MV/m after adding the modified nanoparticles.
 4. The method of claim 1, further comprising modifying nanoparticles to form the modified nanoparticles prior to the adding the modified nanoparticles to the base fluid.
 5. The method of claim 1, wherein the modified nanoparticles improve the at least one property of the fluid as compared to an otherwise identical fluid absent the modified nanoparticles.
 6. The method of claim 1, wherein the modified nanoparticles have at least one functional group selected from the group consisting of a sulfonate, a sulfate, a sulfosuccinate, a thiosulfate, a succinate, a carboxylate, a hydroxyl, a glucoside, an ethoxylate, a propoxylate, a phosphate, an ether, an amine, an amide, a hydrocarbon, and combinations thereof.
 7. The method of claim 1, wherein the modified nanoparticles have at least one covalent modification selected from the group consisting of oxidation; fluorination; free radical additions; addition of carbenes, nitrenes and other radicals; arylamine attachment via diazonium chemistry; and combinations thereof.
 8. The method of claim 1, wherein the improved properties of the fluid may improve the performance of the downhole tools by improving the resolution of these tools as compared to an otherwise identical fluid absent the nanoparticles.
 9. The method of claim 1, wherein the modified nanoparticles have at least one dimension no greater than 1000 nm.
 10. The method of claim 1, wherein the base fluid is selected from the group consisting of a drilling fluid, a completion fluid, a production fluid, and a stimulation fluid.
 11. The method of claim 1, wherein the non-aqueous based fluid is selected from the group consisting of an all oil fluid, a brine-in-oil emulsion, a water-in-oil emulsion, and combinations thereof; wherein the aqueous fluid is selected from the class consisting of a water-based fluid, an oil-in-water emulsion, an oil-in-brine emulsion, and combinations thereof.
 12. The method of claim 1 wherein the amount of modified nanoparticles in the fluid ranges from about 0.0001 wt % to about 15 wt %.
 13. A method comprising: circulating a tuned fluid in a subterranean reservoir wellbore; wherein the tuned fluid comprises a base fluid and an effective amount of modified nanoparticles to improve the at least one property of the fluid; wherein the modified nanoparticles are selected from the group consisting of modified graphene nanoparticles, modified graphene platelets, modified electrically-conductive nanotubes, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof; and wherein the base fluid comprises a non-aqueous based fluid, an aqueous based fluid, and combinations thereof; and wherein the modified nanoparticles are modified by a method selected from the group consisting of chemical modification, covalent modification, functionalization, ionic associations, and combinations thereof; and improving performance of a downhole tool as compared to an otherwise identical fluid absent the modified nanoparticles.
 14. The method of claim 13, wherein the tuned fluid has a resistivity ranging from about 0.02 ohm-m to about 1,000,000 ohm-m; wherein the tuned fluid has a dielectric strength ranging from about 6 MV/m to about 100 MV/m; wherein the tuned fluid has a thermal conductivity ranging from about 0.1 W/m-K to about 1.2 W/m-K, and combinations thereof.
 15. The fluid composition of claim 13, wherein the base fluid is selected from the group consisting of a drilling fluid, a completion fluid, a production fluid, a stimulation fluid, and combinations thereof.
 16. The fluid composition of claim 13, wherein the amount of modified nanoparticles in the base fluid ranges from about 0.0001 wt % to about 15 wt %.
 17. A fluid composition comprising: a base fluid selected from the group consisting of a non-aqueous base fluid, an aqueous base fluid, and combinations thereof; modified nanoparticles selected from the group consisting of modified graphene nanoparticles, modified nanotubes, modified graphene platelets, modified electrically-conductive nanorods, nanospheres, single-walled nanotubes, double walled nanotubes, multiwalled nanotubes, nano-onions, fullerenes, nanodiamonds, and combinations thereof; wherein the modified nanoparticles are modified by a method selected from the group consisting of chemical modification, covalent modification, functionalization, ionic associations, and combinations thereof; and wherein the fluid composition has a resistivity ranging from about 0.02 ohm-m to about 1,000,000 ohm-m, a thermal conductivity ranging from about from about 0.1 W/m-K to about 1.2 W/m-K, a dielectric strength ranging from about 6 MV/m to about 100 MV/m, and combinations thereof.
 18. The fluid composition of claim 17, wherein the base fluid is selected from the group consisting of a drilling fluid, a completion fluid, a production fluid, a stimulation fluid, and combinations thereof.
 19. The fluid composition of claim 17, wherein the amount of modified nanoparticles in the base fluid ranges from about 0.0001 wt % to about 15 wt %. 